On-board vehicle computer systems are known in the art. Such systems monitor and control operations of mechanical vehicle systems, including vehicle engine systems, transmission systems, brake systems, suspension systems, and display systems. On-board computer systems receive information from various sensors, such as engine speed sensors, manifold pressure sensors, etc. The on-board computer systems can control systems such as by controlling mixture, fluid flow, etc., by controlling electronic systems, or by controlling solenoid-actuated valves that regulate flow of hydraulic fluid. One such computerized vehicle system is described in U.S. Pat. No. 4,875,391 to Leising et al. (incorporated by reference). A system for interfacing with a vehicle computer is disclosed in U.S. Pat. No. 5,459,660 to Berra (incorporated by reference); and a system for reprogramming vehicle computers is disclosed in U.S. Pat. No. 5,278,759 to Berra et al. (incorporated by reference). German Patent Document DE 35 40 599 A1 discloses an on-board vehicle computer having a display system that is arranged in an instrument cluster of a dashboard of a vehicle. An on-board computer for a motor vehicle is also disclosed in U.S. Pat. No. 5,150,690 to Ebner et al. (incorporated by reference).
Many vehicles employ several separate microprocessor based computer systems which cooperate with one another. On-board communications systems typically include data busses to enable data communication between such vehicle computer systems. Such data bus technology is disclosed in U.S. Pat. Nos. 4,706,082; 4,719,458; 4,739,323; 4,739,324; and 4,742,349 (all of which are incorporated by reference). Such communications systems may employ multiplexing so that simple wire harnesses can be employed for data transmission. In many vehicles, direct access may be provided to monitored data on a real time basis, so that display tools and engine analyzers may be used to perform a more complete diagnosis of engine problems than can be performed by on-board computers. For example, a data terminal connected to an input/output port of the vehicle computer or to an electronic control module may be provided under a dashboard, as described in U.S. Pat. No. 4,853,850 to Krass, Jr. et al. (incorporated by reference).
Because of heavy reliance on on-board computer systems, vehicles presently sold in the United States provide a standardized diagnostic interface according to a "OBDII/CARB" standards requirement. The OBDII/CARB requirement offers a choice between a J1850 specification and an ISO9141 (International Standards Organization) specification. The OBDII requirement, the J1850 standard, and the ISO9141 specification are incorporated herein by reference.
It is also known to use hand held display tools to display code values generated by vehicle computers. Such hand held display tools are described in U.S. Pat. No. 4,602,127 to Neely et al.